1. Field of the Invention
The present invention relates to a recording medium such as BD-ROM (Blu-ray Disc ROM) which has data written in intermittent or alternate wobbled (or zigzag) pits and an apparatus and methods for forming, recording, and reproducing the recording medium.
2. Description of the Related Art
Recently, the standardization of Blu-ray Disc Rewritable (BD-RE), which is a new high-density rewritable optical disk capable of recording large capacity, high-quality video and audio data, is in progress. BD-RE related products are expected to be available on the market in the near future.
FIG. 1A depicts the structure of a BD-RE, wherein a clamping area, a burst cutting area (BCA), a transition area, a lead-in area, a data area, and lead-out area are disposed in order as shown.
As illustrated in FIG. 1B, the BCA is located in the innermost circumferential area of the BD-RE that is accessed first when the disk is loaded into a reproducing apparatus and may contain an information for the disc, such as serial number and other optional information pre-recorded by disc manufacturer.
The lead-in area may comprise several pre-assigned areas such as a first guard (Guard 1) area, a permanent information & control data (PIC) area, a second guard (Guard 2) area, a second information (Info 2) area, and an optimum power calibration (OPC) area. The Guard 1 area and the PIC area are pre-recorded areas in which some initial data is pre-recorded, whereas the other areas of the lead-in area, the data area, and the lead-out areas are all rewritable areas.
In the PIC area, important permanent disc information is encoded in a wobbled groove by high frequency modulation (HFM).
HFM Grooves may be modulated in the radial direction with a rather high bandwidth signal, to create a data channel for replicated information with sufficient capacity and data rate.
As depicted in FIG. 2, the wobble-shaped data encoding is performed by bi-phase modulation. In this modulation method, a bit with value 0 may be represented by a transition at the start of the bit cell and a bit with value 1 may be represented by a transition at the start and in the middle of the bit cell. The modulated bits may be recorded on the disc by a deviation of the groove from an average centerline as indicated in FIG. 2. The length of each bit cell may be 36T, where T corresponds to the length of a channel bit in the rewritable data areas.
Also, a read-only Blu-ray Disk (BD-ROM) is also under development along with the BD-RE. A BD-ROM may include an inner area, a clamping area, a transition area, an information area, and a rim area, as shown in FIG. 3.
The information area may further comprise a BCA, a lead-in zone, a data zone, a lead-out zone, and an outer zone. As in BD-RE, the BCA may contain disc important information (DII), such as a disc serial number and copy protection information (CPI). If a BD-ROM is copy protected, the DII may be required to decrypt the main data contained on the BD-ROM.
The disc information in the PIC zone may be recorded as straight pits in the same way as main data such as audio/video (A/V) streams are recorded in the data zone. The disc information may be 17PP-modulated data written in the form of an error correction code (ECC) block of size 64 KB, for example.
In this case, however, it takes some demodulation time to retrieve the disc information from the BD-ROM because the disc information may be demodulated by an RF signal detection method.
As described above, the disc information contained in the PIC area of a BD-RE may be encoded in a wobbled groove by HFM. If the disc information is recorded in the PIC zone of a BD-ROM as straight pits, an optical disk reproducing apparatus should be able to apply different detecting schemes to obtain the disc information depending on the disk type (BD-RE or BD-ROM). Unless the correct scheme is chosen, the optical disk reproducing apparatus will fail to detect the disc information. For example, if a method for detecting BFM-modulated disc information encoded in a wobbled groove of a BD-RE is applied to a BD-ROM, the optical disk reproducing apparatus will not be able to retrieve the disc information which is recorded in the PIC zone as straight pits.
In addition, if the disc important information (DII) contained in the BCA cannot be retrieved due to a read error, it is impossible to retrieve the data recorded on the disk. For example, if an error occurs while the copy protection information (CPI) is retrieved from the BCA, it may be impossible to reproduce the main data recorded in the data zone because the data cannot be decrypted.
Also, because the copy protection information (CPI) recorded on PIC area of the disk includes important data, e.g., key data to decrypt encrypted main data recorded on the data zone, it should not be detected easily by any illegal device and copied to other recording media to protect the encrypted contents recorded on the disk. It should be only detected by a desired detection method in a legally permitted device to ensure robustness.